JP7195909B2 - Sheet feeding device, image reading device and image forming device - Google Patents

Description

The present invention relates to a sheet feeding device that feeds a sheet, an image reading device that reads image information from a sheet, and an image forming device that forms an image on a sheet.

A sheet feeding device for feeding sheets used as recording materials or originals in image forming apparatuses such as printers, copiers, and multifunction machines includes a feeding member that feeds sheets from a tray and a sheet feeding member that feeds sheets one by one. and a separating member for separating the sheets. In general, in order to stably feed sheets, it is preferable that the pressing force of the feeding member against the sheets is within a certain range close to the designed value. If the pressure of the feeding member against the sheet is too high, for example, the next sheet overlapping the uppermost sheet with which the feeding member is in contact moves toward the separating member and bends in contact with the separating member. This increases the possibility that the next sheet will be folded. If the pressure applied by the feeding member is too low, the sheet conveying resistance is greater than the force with which the feeding member tries to convey the sheet, and conveying defects tend to occur.

In Patent Document 1, based on a detection signal from a sensor that detects the occurrence of sheet feeding failure or double feeding, the length of a compression spring that urges the pickup roller downward is changed by a cam mechanism. It is described that the pressure of the

Japanese Unexamined Patent Application Publication No. 2008-19069

However, in the configuration described in Patent Document 1, the provision of the cam mechanism and the control circuit for controlling the operation of the cam mechanism complicates the device, leading to an increase in cost.

SUMMARY OF THE INVENTION Accordingly, it is an object of the present invention to provide a sheet feeding apparatus, an image reading apparatus, and an image forming apparatus that are capable of stably feeding sheets with a simple configuration.

According to one aspect of the present invention, a sheet stacking portion on which sheets are stacked, a stacking position for stacking the sheets on the sheet stacking portion, and a sheet stacking portion for feeding the sheets on the sheet stacking portion are provided. a feeding position above the stacking position of the sheet stacking portion; and a holding member for holding the feeding member . between a first position where the feeding member contacts the sheet on the sheet stacking portion and a second position below the first position where the feeding member contacts the sheet on the sheet stacking portion; a holding member that allows the feeding member to move; a lever member that has an abutting portion that abuts on the holding member and rotates around a rotation shaft; an elastic member for biasing the holding member toward the first position ; a detection unit for detecting a part of the holding member to detect the position of the upper surface of the sheet stacked on the sheet stacking unit; a control unit that controls the driving source based on the detection result of the detection unit , wherein the feeding member is positioned at the first position when viewed from the axial direction of the rotation shaft of the lever member. The distance from the rotating shaft to the line of action of the force applied by the elastic member to the lever member when the feeding member is at the second position is the distance from the rotating shaft to the line of action when the feeding member is positioned at the second position. The sheet feeding device is characterized in that the elastic member is arranged so as to be shorter than the distance .

According to the present invention, it is possible to achieve stable sheet feeding with a simple configuration.

1 is a schematic diagram of an image forming apparatus according to an embodiment of the present disclosure; FIG. Schematic diagram of an image reading device. FIG. 3 is a block diagram showing the control system of the ADF; 4 is a flowchart showing a control method for document feeding operation; FIG. 2 is a schematic diagram showing the image reading device with the cover unit opened; 4 is a perspective view of the feeding unit of the ADF; FIG. 4 is a perspective view of the cover unit from which the feeding unit is removed; FIG. 4 is a perspective view of the cover unit to which the feeding unit is attached; FIG. FIG. 4 is a perspective view of the cover unit to which the feeding unit is attached, viewed from another direction; FIG. 4 is a diagram for explaining the arrangement of pressure springs; 4A to 4C are diagrams showing arrangement examples (a to c) of pressure springs; Graphs (a to i) for explaining changes in pressure with respect to displacement of the feeding roller in the arrangement example of FIG. 4A and 4B are diagrams for explaining arrangement conditions of pressure springs; FIG. The figure which shows the modification (a, b) of this embodiment.

Exemplary embodiments of the invention are described below with reference to the drawings.

FIG. 1 is a schematic diagram of an image forming apparatus 300 according to this embodiment. The image forming apparatus 300 includes an image forming unit 301 , an image reading unit 200 arranged above the image forming unit 301 , and an auto document feeder (hereinafter referred to as ADF) placed on the image reading unit 200 . ) 100. The image forming unit 301 forms an image on a sheet P used as a recording medium based on image information input from an external PC or image information read from a document by the image reading unit 200 . Sheets used as recording media or documents include paper such as paper and envelopes, plastic film for overhead projectors, and cloth.

The image forming section 301 has an intermediate transfer electrophotographic unit 10 including four image forming stations PY, PM, PC, PK, an intermediate transfer belt 31 and a fixing device 40 . Each image forming station PY to PK forms a toner image on the surface of the photosensitive drum 11 by an electrophotographic process. That is, when the image forming stations PY to PK are requested to form a toner image, the photosensitive drum 11, which is a photosensitive member, is rotationally driven, and the charging device uniformly charges the surface of the photosensitive drum 11. FIG. The exposure device 13 irradiates the photosensitive drum 11 with laser light based on image information to expose the surface of the drum and writes an electrostatic latent image on the photosensitive drum 11 . The developing device 14 supplies charged toner particles to the photosensitive drum 11 to develop the electrostatic latent image into a toner image. The toner images of respective colors formed by the image forming stations PY to PK are primarily transferred from the photosensitive drum 11 to the intermediate transfer belt 31 by the primary transfer roller 17 . Attached matter such as toner remaining on the photosensitive drum 11 is removed by the drum cleaner 15 .

An intermediate transfer belt 31, which is an intermediate transfer member, is wound around a secondary transfer inner roller 34, a tension roller 38, and a tension roller 32, and is driven to rotate counterclockwise in the figure. The toner image carried on the intermediate transfer belt 31 is transferred to the sheet P at the secondary transfer portion T2, which is a nip portion between the intermediate transfer belt 31 and the secondary transfer roller 35 facing the inner secondary transfer roller 34. be transcribed. Attached matter such as toner remaining on the intermediate transfer belt 31 is removed by a belt cleaner 36 .

The sheet P to which the toner image has been transferred is delivered to the fixing device 40 . The fixing device 40 has a fixing roller 40a and a pressure roller 40b for nipping and conveying the sheet P, and a heat source such as a halogen heater for heating the fixing roller 40a. The fixing device 40 fuses the toner by applying heat and pressure to the toner image while conveying the sheet P, and then fixes the image on the sheet P by fixing the toner.

Sheets P are fed one by one from the cassette 20 in parallel with such an image forming process. A sheet P fed from the cassette 20 by a feeding roller 21 , which is an example of a feeding member, is fed while being separated from other sheets by a separating member such as a separating roller or a separating pad. transported by After that, the pre-registration roller 22 abuts the leading edge of the sheet against the stopped registration roller 23 , thereby correcting the skew of the sheet P. FIG. The registration rollers 23 feed the sheet P to the secondary transfer portion T2 at timing that matches the progress of the image forming process by the electrophotographic unit 10 . The sheet P on which an image is formed by passing through the secondary transfer portion T2 and the fixing device 40 is conveyed to the discharge roller 41 via the conveying rollers 42 and 43, and is discharged to a discharge tray provided above the image forming portion 301. 49 is discharged.

In the above description, the electrophotographic unit 10 is an example of image forming means, and may be a direct transfer type electrophotographic unit that directly transfers a toner image from a photosensitive member to the sheet P, or an inkjet type or offset printing type image forming unit. A unit may be used.

(Image reader)
The ADF 100, which is the sheet feeding device of this embodiment, and the image reading section 200, which constitutes the image reading device of this embodiment together with the ADF 100, will be described with reference to FIG.

The image reading section 200 has a platen glass 218 , a document table glass 219 and a reading unit 201 . The reading unit 201 has a lamp 202 and a mirror 203 mounted on a carriage 204 that can move in the sub-scanning direction (horizontal direction in the figure) under the platen glass 219 . The lamp 202 is a light source for irradiating the image surface of the document S with light. Reflected light from the document S is guided to an imaging lens 207 via mirrors 203, 205, and 206, and forms an image on a charge-coupled device 208 as an imaging device. The charge-coupled device 208 converts incident light into electronic image information by performing photoelectric conversion.

The reading unit 201 of the image reading section 200 can perform image reading operations in two modes of fixed reading and skimming. Fixed reading is an operation of reading image information from a stationary original placed on the platen glass 219 while the reading unit 201 moves in the sub-scanning direction. Skimming is an operation of reading image information from one sheet surface of a moving original conveyed by the ADF 100 while the reading unit 201 is positioned below the platen glass 218 .

The ADF 100 includes a reading unit 124 , a document tray 111 , a feeding unit 143 , a registration roller pair (hereinafter referred to as a registration roller pair) 121 , conveying roller pairs 122 , 123 , 125 , a discharge roller pair 116 and a discharge tray 119 . there is

The reading unit 124 reads image information from the other sheet surface of the moving document conveyed by the ADF 100 . That is, both the reading unit 201 of the image reading section 200 and the reading unit 124 of the ADF 100 are examples of image reading means for reading image information from a sheet. In the present embodiment, a contact image sensor is used as the reading unit 124, and the reading unit 124 is provided with a lamp serving as a light source, a lens array forming an equal-magnification optical system, and an imaging device such as CMOS.

Documents S whose images are to be read are placed on a document tray 111, which is a sheet stacking unit of the present embodiment. The widthwise position of the document S placed on the document tray 111 is regulated by a side regulating plate 110 that is movable in the widthwise direction. Further, the lower surface of the document tray 111 is supported by a lift plate 145, which is an example of lifting means. The lift plate 145 is rotated by being driven by a tray lifting motor 181 (FIG. 3), which is a drive source, to lift up and down the document tray 111 .

The feeding unit 143 has a feeding roller 101 , a conveying roller 103 and a separating roller 104 . The feeding roller 101 is arranged above the document tray 111 and feeds the document S from the tray. The transport rollers 103 receive the document S from the feeding roller 101 and transport it toward the registration roller pair 121 .

The separation roller 104 is a roller connected to a fixed shaft via a torque limiter, and separates the document S by applying a frictional force to the document S that has entered the separation nip between the conveying roller 103 and the separation roller 104 . do. When one document S enters the separation nip, the torque limiter slips and the separation roller 104 rotates following the conveying roller 103 . On the other hand, when a plurality of documents enter the separation nip, the separation roller 104 does not rotate and the conveyance of the sheets other than the uppermost sheet in contact with the conveyance roller 103 is stopped. The separation roller 104 is an example of a separation member, and a retard roller to which rotation in a direction opposite to sheet conveyance is input via a torque limiter, or a pad-like friction member may be used.

After passing through the separation nip, the document S is abutted against the stationary registration roller pair 121 and corrected for skew. It is transported towards unit 124 . When the document S passes between the platen glass 118 of the reading unit 124 and the platen glass 218 of the image reading unit 200, image information is read by the reading units 124 and 204 from one side and the other side of the document S. . After that, the document S is delivered to the discharge roller pair 116 via the transport roller pair 125 and discharged to the discharge tray 119 by the discharge roller pair 116 .

(control system)
A configuration for controlling the ADF 100 will be described with reference to FIG. The control means for controlling the ADF 100 consist of a control circuit with at least one processor. A control unit 50, which is a control means of the present embodiment, includes a central processing unit (CPU) 51, a read-only memory (ROM) 52 which is an example of a nonvolatile storage medium, and a random memory which is an example of a volatile storage medium. and access memory (RAM) 53 . The CPU 51 reads out and executes programs stored in the ROM 52 or the like, and controls operations of the ADF 100 and the image reading section 200 . The RAM 53 serves as a work space when the CPU 51 executes programs. Each function of the control unit 50 described below may be implemented on the circuit of the control unit as independent hardware such as an ASIC, and may be implemented as a functional unit of a program executed by the CPU 51 or other processing device in terms of software. may be implemented in

The ADF 100 is provided with various sensors for detecting the state of the apparatus. The feeding position sensor 191 is a sensor for detecting that the upper surface of the document stacked on the document tray 111 is at a position where the document can be fed by the feeding roller 101 . A multi-feed detection sensor 192 detects a multi-feed state in which a plurality of documents have entered the separation nip. Specifically, a sensor that detects the document between the separation nip and the pair of registration rollers 121 in the sheet feeding direction can be used as the double-feed detection sensor 192 . A document detection sensor 193 is a sensor that detects the presence or absence of a document on the document tray 111 . As each of the sensors 191 to 193, a photoelectric sensor (photointerrupter) can be used which is shielded by a flag that swings when pressed by the document. For example, the document detection sensor 193 is arranged so as to be shielded from light when the document detection flag 129 (FIG. 2) is pressed by the document S and rotated.

The CPU 51 controls the operations of the motors 181 to 183 that are driving sources of the ADF 100 by sending drive commands to the driver 54 . A tray lift motor 181 drives the lift plate 145 described above. A feeding motor 182 drives the feeding roller 101 and the conveying roller 103 of the feeding unit 143 . The feeding roller elevating motor 183 can move the feeding roller 101 between a position where the feeding roller 101 can contact the documents stacked on the document tray 111 and a retracted position so as not to contact the documents. In this embodiment, these motors 181-183 are stepping motors. The CPU 51 can control the amount and speed of rotation of the motors by designating the number and frequency of the excitation pulses that the driver 54 supplies to the motors 181-183. The driver 54 can also rotate the motors 181 to 183 in opposite directions.

The control unit 50 is connected to the main body control unit 350 mounted on the image forming unit 301 via the communication IC 59 . The main control unit 350 is composed of a control circuit having at least one processor, and controls the image forming operation by the electrophotographic unit 10 and the conveying operation of the sheet P as the recording material. The body control unit 350 receives image information read by the image reading device, and executes a job of forming a copy image on the sheet P based on the image information. Further, the main control unit 350 also serves as a control unit that performs integrated control of the image forming apparatus 300. For example, based on instructions given by the user via the operation unit, the main control unit 350 sends commands to the control unit 50 to control the operation of the image reading apparatus. to control.

FIG. 4 is a flow chart showing a method of controlling the document feeding operation by the ADF 100. As shown in FIG. When a command signal (reading start command) commanding reading of image information is sent from the body control unit 350 to the control unit 50 (S1: Y), the CPU 51 starts lifting up the document tray 111 (S2). That is, the CPU 51 sends a driving command to the driver 54 to start driving the tray lifting motor 181 , and the driver 54 supplies an excitation pulse to the tray lifting motor 181 to rotate the tray lifting motor 181 . As a result, lift plate 145 rotates to lift document tray 111 .

When the upper surface of the document stacked on the document tray 111 abuts against the feeding roller 101 and the arm 102 is lifted, part of the arm 102 (a flag portion 190 described later) shields the feeding position sensor 191 (S3: Y). That is, the feeding position sensor 191 detects that the upper surface of the document reaches a predetermined height (hereinafter referred to as the detection position of the feeding position sensor 191). After the feeding position sensor 191 detects the document, the tray lifting/lowering motor 181 continues to be driven for a predetermined number of pulses (S4) and then stopped (S5).

When the lift-up of the document tray 111 is completed, the feeding motor 182 is started to be driven, and the document is fed from the document tray 111 by the feeding roller 101 to start feeding the document (S6). When the number of documents on the tray decreases due to document feeding, the positions of the feeding roller 101 and the arm 102 are lowered, and the feeding position sensor 191 may switch to a state in which no document is detected (S7: Y). . In this case, the process returns to S2 and the drive of the tray lifting motor 181 is started again, and the document tray 111 is lifted up from the detection position to a position above the detection position by a predetermined number of pulses, and document feeding is continued. When the document detection sensor 193 detects that there are no more documents on the tray (S8: Y), the CPU 51 rotates the tray lifting/lowering motor 181 in the opposite direction to lift down the document tray 111 (S9), and terminates the process. .

In the above control method, the reason why the lift-up of the document tray 111 is continued for a predetermined number of pulses even when the upper surface of the document exceeds the detection position of the feeding position sensor 191 is to reduce the noise of the ADF 100 . That is, if the lift-up of the document tray 111 is completed immediately after the feeding position sensor 191 detects the document, the lift-up of the document tray 111 is repeated every time a small number of documents are fed, causing the driving sound of the motor and the tray to be lifted. A moving sound is generated. On the other hand, even if the position of the upper surface of the document slightly changes, if the width of the change is small enough not to affect the feeding by the feeding roller 101, the feeding operation can be continued without any problem. Therefore, the noise can be reduced by lifting the document tray 111 upward by a certain distance from the detection position of the feeding position sensor 191 .

(Feeding unit)
The configuration of the feeding unit 143 of the ADF 100 will be described in detail with reference to FIGS. 5 to 9. FIG. FIG. 5 shows how the cover unit 140 supporting the feeding unit 143 is opened. A cover body 141 of the cover unit 140 is supported by a frame 144 of the ADF 100 via a rotation shaft 146 and can be opened and closed by rotating about the rotation shaft 146 . The cover unit 140 is provided with a feed unit 143, rollers on one side of the pair of registration rollers 121 and the pair of transport rollers 122, and a guide that forms a document transport path. The cover unit 140 is opened when replacing or cleaning the feeding unit 143 or when removing a document jammed inside the ADF 100 . Further, the cover unit 140 can be kept open at a predetermined angle by a stopper, and the feeding unit 143 can be removed from the cover main body 141 in the right direction (arrow D1) in the figure.

6 is a perspective view of the feeding unit 143. FIG. A feeding roller 101 , which is a feeding member of this embodiment, is supported by a shaft 113 attached to an arm 102 . The arm 102, which is the holding member of the present embodiment, is rotatable about a shaft 105 holding the conveying roller 103 so as to vertically move the feeding roller 101 when the cover unit 140 is closed. The feeding roller 101 and the conveying roller 103 are connected via pulleys 108 and 109 and a timing belt 107 stretched around these pulleys. A pin 147 for inputting driving force is provided at the end of the shaft 105 . Rotation input to the shaft 105 via the pin 147 is distributed to the feed roller 101 and the transport roller 103 . The belt drive having the timing belt 107 is an example of a transmission mechanism.

Bearings 148 a and 148 b are fitted to the shaft 5 on both sides of the conveying roller 103 in the axial direction of the shaft 5 . Further, the arm 102 is provided with a flag portion 190 that shields the feeding position sensor 191 and a pressing portion 163 that is pressed by a lever member, which will be described later.

FIG. 7 is a perspective view (viewed from the downstream side of arrow D1 in FIG. 5) showing the cover unit 140 with the feeding unit 143 removed. A drive shaft 150 that transmits driving force to the feeding unit 143 is held by the cover body 141 , an input gear 149 is attached to one end of the drive shaft 150 , and a coupling 151 is provided to the other end of the drive shaft 150 . The cover main body 141 is provided with positioning grooves 152 a and 152 b corresponding to the bearing portions 148 a and 148 b of the feeding unit 143 . A unit holding portion 153 made of resin is provided at a position corresponding to the bearing portion 148 a , and a concave portion 156 for receiving the flag portion 190 of the arm 102 is provided near the feeding position sensor 191 .

When attaching the feeding unit 143, as shown in FIG. 8, the shaft 105 is inserted into the coupling 151 so that the pin 147 is held at a predetermined position, and the unit holding portion 153 is bent to move the bearing portion 148a to the unit holding portion 153. fit in. At this time, the bearing portions 148a and 148b of the feeding unit 143 are engaged with the positioning grooves 152a and 152b of the cover unit 140, thereby determining the position of the feeding unit 143 in the sheet feeding direction. Also, the flag portion 190 of the arm 102 is accommodated in the recess 156 .

As shown in FIG. 9, the convex portion 157 provided on the arm 102 is engaged with the opening portion 158 of the cover body 141, so that the position of the feeding unit 143 in the axial direction (the width direction of the document) in the mounted state is adjusted. is determined. The convex portion 157 and the opening portion 158 also serve as stoppers that limit the rotation range of the arm 102 . However, FIG. 9 shows the cover unit 140 to which the feeding unit 143 is attached as viewed from the back side of FIG. 8, and part of the cover main body 141 is omitted.

When the cover unit 140 is closed while the feeding unit 143 is attached to the cover main body 141 , the conveying roller 103 is pressed against the separation roller 104 . Then, the bearing portions 148a and 148b of the feeding unit 143 hit the deepest portions of the positioning grooves 152a and 152b of the cover body 141, and the position of the feeding unit 143 in the height direction is determined.

(Pressure lever)
Here, a configuration for pressing the feeding roller 101 against the document will be described. In this embodiment, as shown in FIG. 9 , a pressure lever 154 connected to a pressure spring 155 presses the arm 102 to bring the feed roller 101 into pressure contact with the documents stacked on the document tray 111 . In other words, the biasing force of the pressure spring 155, which is an example of an elastic member, does not directly act on the arm 102 holding the feed roller 101, but is applied via the pressure lever 154, which is an example of a lever member. configured to work.

As shown in FIG. 7, the pressure lever 154 and the pressure spring 155 are held by the cover body 141 and remain on the cover unit 140 even when the feeding unit 143 is removed. This configuration is advantageous in that replacement work can be facilitated compared to a configuration that requires, for example, attachment and detachment of a spring member directly connected to the arm 102 when replacing the feeding unit 143 . The pressure lever 154 and the pressure spring 155 are covered by the protective plate 141a of the cover body 141 so that only the tip portion 162 of the pressure lever 154, which is the contact portion of the pressure lever 154 against the arm 102, is exposed. It is

As shown in FIG. 9, the pressurizing lever 154 is held by lever holding portions 159a and 159b of the cover body 141 via a rotating shaft 164, and rotates around the rotating shaft 164. As shown in FIG. The rotation shaft 164 is parallel to the document feeding direction D2 by the feeding roller 101 when viewed in the thickness direction of the document fed by the feeding roller 101 (substantially vertical direction when the cover unit 140 is closed). extends to The pressing lever 154 extends from the rotary shaft 164 in a direction that intersects the feeding direction D2 (especially in the document width direction), and abuts on the pressing portion 163 of the arm 102 at the leading end portion 162 . The contact position of the tip portion 162 and the pressing portion 163 in the feeding direction D2 overlaps the range of the feeding roller 101 in the feeding direction D2.

The pressure spring 155 of this embodiment is a tension coil spring, one end (free end 155a) is attached to the lever-side mounting portion 160 of the pressure lever 154, and the other end (fixed end 155b) is the cover main body. It is attached to the cover side attachment 161 of 141 . The contact portion between the free end 155a and the lever-side mounting portion 160 is the point of action of the force acting on the pressure lever 154 from the pressure spring 155. As the pressure lever 154 rotates, the pivot shaft 164 is centered. and move along the arc. On the other hand, the fixed end 155b is fixed to the cover main body 141 that constitutes the housing of the ADF 100 together with the frame 144. As shown in FIG. The length of the pressure spring 155 is the distance between the free end 155a and the fixed end 155b.

The pressure spring 155 pulls the pressure lever 154 in a direction (clockwise direction in the drawing) that causes the pressure lever 154 to press the arm 102 downward, thereby biasing the arm 102 downward via the pressure lever 154 . do. In addition, the pressure spring 155 dissipates the bounce of the feed roller 101 due to the impact when the feed roller 101 and the upper surface of the document come into contact with the friction at the contact portion with the mounting portions 160 and 161, thereby feeding the document. It has a function to quickly stabilize the pressure in time for the start of the operation. The pressing force of the feeding roller 101 against the document is mainly due to the force of the pressing lever 154 pressing the arm 102 downward and the gravity acting on the feeding unit 143 due to the weight of the feeding roller 101, the arm 102, and the like. determined. The pressing force of the feeding roller 101 is set, for example, within a range of 140 gf to 160 gf.

The lower limit of the pressing force is determined in consideration of the ability to handle top-folded originals. A top-folded document is a sheet in which the edges of the document are bent upward or curved, and is likely to receive greater transport resistance than usual by contacting a guide or the like at a position other than the feeding roller 101 . If the pressing force of the feed roller 101 is insufficient, the frictional force generated between the feed roller 101 and the document becomes smaller than the transport resistance received by the document, which leads to the feed roller failure. Slip of 101 is likely to occur.

On the other hand, the upper limit of the pressing force is determined so as not to damage the document. When the pressure is too high, even the document (the next document) overlapping the uppermost document with which the feeding roller 101 is in contact moves toward the separation nip, and the separation nip and the feeding roller 101 are separated from each other. In between, the next document is bent. Thereafter, when the next document is fed, the bent portion is crushed by the separation nip, causing damage such as folding of the document. Such damage is likely to occur when the document is a sheet material with low rigidity such as thin paper. is set to

The pressing portion 163 of the arm 102 is provided outside the range of the upper surface of the arm 102 that overlaps the feeding roller 101 in the axial direction of the feeding roller 101 . located at a relatively low position. In particular, it is preferable to provide the pressing portion 163 below the upper end position of the feeding roller 101 . As a result, the vertical range occupied by the pressure lever 154 and the feeding unit 143 is reduced, and the pressure lever 154 can be arranged inside the cover main body 141 (that is, near the ceiling of the ADF 100) without difficulty. be.

With respect to the sheet feeding direction, the contact position between the pressing portion 163 and the pressure lever 154 is the position of the feeding roller 101 (the range from the upstream end position to the downstream end position of the roller in the sheet feeding direction). ). Further, it is preferable that the contact position between the pressing portion 163 and the pressure lever 154 be as close as possible to the feeding roller 101 in the axial direction of the feeding roller 101 . If the contact position is distant from the feeding roller 101, there is a concern that the contact pressure of the feeding roller 101 against the document becomes uneven due to the deformation of the arm 102. Contributes to stabilizing pressure.

(Arrangement of pressure spring)
Here, the arrangement of the pressing lever 154 and the pressing spring 155 for suppressing fluctuations in the pressing force of the feeding roller 101 will be described. FIG. 10 shows the positional relationship among the pressurizing lever 154, the pressurizing spring 155 and the arm 102 viewed in the axial direction of the rotating shaft 164 of the pressurizing lever 154. As shown in FIG.

Among the factors that define the magnitude of the pressure K applied to the document S by the feeding roller 101, gravity generated by the weight of the feeding roller 101 and the like is substantially constant. On the other hand, the magnitude of the pressing force J with which the pressing lever 154 presses the arm 102 is an amount that can vary according to the angle of the pressing lever 154 .

Regarding the pressing force J, the following relationship holds.
M=J・I=F・H (Equation 1)
However, M represents the counterclockwise moment in the figure acting on the pressing lever 154 by the restoring force F of the pressing spring 155 . I represents the distance from the rotation axis of the pressure lever 154 to the contact position between the pressure lever 154 and the arm 102 . H is the distance from the rotation axis of the pressing lever 154 to the line of action G of the restoring force F (that is, the arm length of the moment M). A line of action G of the restoring force F is a straight line drawn in the direction of the restoring force F through the free end 155 a of the pressure spring 155 .

Rewriting Equation 1, we get:
J=F H/I (Formula 2)
As can be seen from the above formula, in order to suppress fluctuations in the pressing force J, it is important to reduce the change in the moment M (=F·H) with respect to the rotation of the pressure lever 154. .

In the following description, the state in which the feeding roller 101 is at a predetermined position where the document can be fed (that is, a predetermined target position so that the sheet can be properly fed) is used as a reference. Consider the change in the moment M when the feed roller 101 is displaced vertically. The target position in this embodiment is a preset position between the detection position of the feed position sensor 191 and the position where the lift-up ends (the position further lifted up by a predetermined number of pulses from the detection position). Point. In other words, the detection position of the feeding position sensor 191 and the value of the predetermined number of pulses in the feeding operation are set in accordance with the preset target position.

When the feed roller 101 is displaced upward from the target position, the restoring force F of the pressure spring 155 becomes greater than when the feed roller 101 is at the target position. On the other hand, when the feed roller 101 is displaced downward from the target position, the restoring force F of the pressure spring 155 becomes smaller than when the feed roller 101 is at the target position. Therefore, by arranging the pressure spring 155 so as to offset the change in the restoring force F, it is possible to suppress the change in the moment M when the feeding roller 101 is displaced from the target position.

FIGS. 11A to 11C are diagrams for explaining conditions regarding the placement of the pressure spring 155. FIG. In the arrangement (example 1) of FIG. 11A, the fixed end 155b is located on the opposite side of the pivot shaft 164 of the pressing lever 154 with respect to the reference line T0. However, the reference line T0 is a tangential line passing through the position of the lever-side mounting portion 160 when the feeding roller 101 is at the target position of the circle C drawn by the lever-side mounting portion 160 as the pressure lever 154 rotates. be. 11B and 11C (examples 2 and 3), the fixed end 155b is located on the same side as the rotary shaft 164 of the pressure lever 154 with respect to the reference line T0. However, in Example 2 and Example 3, the position of the fixed end 155b is different, and the values of the angles θ1 and θ2 formed by the reference line T0 and the line of action G of the restoring force F are different (0<θ1<θ2<π/ 2).

FIG. 12 shows the length L of the pressure spring 155 and the line of action G of the restoring force F from the rotation shaft 164 when the feed roller 101 is displaced from the target position under the arrangements of Examples 1 to 3. 15 is a graph showing results obtained by calculation of a distance H between , and a pressing force J of a pressure lever 154. FIG. Columns (a, d, g) correspond to example 1 in FIG. 11(a), columns (b, e, h) correspond to example 2 in FIG. 11(b), and columns (c, f, i ) corresponds to example 3 in FIG. 11(c). The horizontal axis of each figure is common, and represents the amount of displacement (unit: mm) of the feeding roller 101 with respect to the target position with a positive sign representing upward displacement. Also, the length L of the pressure spring 155 is the sum of the natural length L0 and the extension amount L1 (L=L0+L1).

Here, the target value of the pressure K of the feeding roller 101 against the document is 150 gf, and the pressure generated by the weight of the feeding roller 101 and the like is 65 gf. Therefore, it is preferable that the pressing force J of the pressing lever 154 is maintained at a value close to 85 gf.

In common with Examples 1 to 3, when the feed roller 101 is displaced upward from the target position, the pressure spring 155 expands more, the length L increases, and the feed roller is displaced downward from the target position. Then, the amount of elongation of the pressure spring is reduced, and the length L is reduced (FIGS. 12(a to 12c)). That is, when the feeding roller 101 is displaced upward from the target position, the restoring force F of the pressure spring 155 increases, and when the feeding roller 101 is displaced downward from the target position, the restoring force F of the pressure spring 155 decreases.

In example 1, the tendency of increase/decrease of the distance H with respect to the displacement of the feeding roller 101 matches the tendency of increase/decrease of the length L of the pressure spring 155 (FIG. 12(d)). Then, as shown in (Equation 2), since the pressing force J is proportional to the product of the restoring force F and the distance H, the change in the distance H with respect to the displacement of the feeding roller 101 is It acts in the direction of increasing the fluctuation range of the pressure J. As shown in FIG. 12G, in the configuration of Example 1, the pressing force J fluctuated within a range of about ±11 gf while the feed roller 101 was displaced ±4 [mm] from the target position.

On the other hand, in Examples 2 and 3, in which the fixed end 155b is positioned on the same side as the rotation shaft 164 with respect to the reference line T0, the tendency of increase or decrease in the distance H with respect to the displacement of the feeding roller 101 is This is contrary to the tendency of increase and decrease of the length L of (Fig. 12(e, f)). That is, the distance H decreases when the feed roller 101 is displaced upward from the target position, and the distance H increases when the feed roller 101 is displaced downward from the target position. Such a change in the distance H cancels out the change in the restoring force F with respect to the displacement of the feeding roller 101, and acts in the direction of suppressing the fluctuation range of the pressing force J. FIG. As shown in FIGS. 12(h, i), in the configurations of Examples 2 and 3, the fluctuation range of the pressing force J while the feeding roller 101 is displaced from the target position by ±4 [mm] is about ±0.2 gf. , ±9 gf.

Since the fixed end 155b is located on the same side of the reference line T0 as the rotating shaft 164, the increase/decrease in the restoring force F and the increase/decrease in the distance H are contradictory. can.

FIGS. 13A and 13B are schematic diagrams for explaining changes in the distance H as the pressure lever 154 rotates. In FIG. 13A, the fixed end 155b is on the same side of the reference line T0 as the rotation shaft 164, and in FIG. It represents the case on the side.

Ignoring physical interference, when the free end 155a of the pressure spring 155 moves on the circle C from the point P1 toward the point P0 in FIG. It can be seen that the distance H to the line G increases monotonically. However, the point P0 is the position of the free end 155a when the line of action G passes through the rotation axis of the pressure lever 154, and the distance H is the minimum (H=0) at this point. The point P1 is the position of the free end 155a when the line of action G is tangential to the circle C. At this time, the distance H is the maximum (the distance from the rotation shaft 164 to the free end 155a).

In the arrangement in which the fixed end 155b is on the same side as the rotation shaft 164 with respect to the reference line T0, the free end 155a is located between points P1 and P0 when the feed roller 101 is at the target position. However, the point P1 to the point P0 is the arc of the circle C from the point P1 to the point P0 in the direction of urging the feed roller 101 downward (that is, clockwise in the drawing). point to The fixed end 155b is provided with a pressure lever 154 in a direction to press the arm 102 downward with respect to a straight line N connecting the free end 155a and the rotary shaft 164 when the feed roller 101 is at the target position. It is assumed to be arranged so as to be biased (that is, to the lower side of the straight line N in the drawing).

The pressure lever 154 is represented by a solid line when the feed roller 101 is at the target position, and the value of the distance H from the rotary shaft 164 to the line of action G1 at this time is "H1". When the feeding roller 101 is displaced below the target position and the pressure lever 154 moves to the position indicated by the dashed line, the free end 155a of the pressure spring 155 approaches the point P0 where the distance H is the minimum. value becomes smaller (H0<H1). On the other hand, when the feeding roller 101 is displaced above the target position and the pressure lever 154 moves to the position indicated by the broken line, the free end 155a of the pressure spring 155 approaches the point P1 where the distance H is maximum. becomes smaller (H2>H1).

On the other hand, as shown in FIG. 13(b), when the fixed end 155b is on the opposite side of the reference line T0 to the rotating shaft 164, the point P0 at which the distance H is minimum and the point P0 at which the distance H is maximum The positional relationship of P1 is reversed. That is, when the pressurizing lever 154 rotates counterclockwise in the figure, the distance H monotonously decreases opposite to the case of FIG. 13(a). Therefore, when the feeding roller 101 is displaced downward from the target position and the pressing lever 154 moves to the position indicated by the dashed line, the free end 155a of the pressing spring 155 approaches the point P0 where the distance H becomes maximum. , the value of the distance H increases (H0>H1). On the other hand, when the feeding roller 101 is displaced above the target position and the pressure lever 154 moves to the position indicated by the broken line, the free end 155a of the pressure spring 155 approaches the point P1 where the distance H is the minimum. The value of the distance H becomes smaller (H2<H1). That is, when the feeding roller 101 is positioned at the first position, the distance H is smaller than when the feeding roller 101 is positioned at the second position below the first position.

(Effect of this embodiment)
By the way, an elastic member such as the pressure spring 155 for applying pressure to the sheet by the feed roller generally has a restoring force corresponding to the designed pressure when the feed roller is at the target position. Designed to give power. However, due to a variety of factors, including manufacturing tolerances and how the feed motion is controlled, the actual magnitude of the restoring force applied by the elastic member may deviate from the desired value. If the pressing force of the feeding roller fluctuates greatly due to such fluctuations in the restoring force, there is a possibility that the sheet may be folded or the sheet may be improperly conveyed.

The reason for the manufacturing tolerance is that the tolerance of the member interposed between the feeding roller and the elastic member, the holding structure of the feeding roller, and the sensor structure for positioning the feeding roller at the target position are cumulative. It refers to changing the magnitude of the restoring force by acting dynamically. For example, the tolerance of each part of the document tray 111 and the feeding unit 143 of this embodiment and the positioning accuracy of the cover unit 140 and the frame 144 of the ADF may cause the height deviation of the pressing portion 163 when starting the feeding operation. It is an element that makes

Further, the reason for the control method of the feeding operation means that the upper surface of the sheet deviates from the target position during the execution of the feeding operation. For example, as described with reference to FIG. 4, in the feeding operation of this embodiment, the upper surface of the document fluctuates between the detection position of the feeding position sensor 191 and the lift-up end position above the detection position. It is allowed. At this time, in the conventional configuration, fluctuations in the restoring force of the elastic member due to changes in the height of the document are directly reflected in fluctuations in the pressing force of the feeding roller 101 .

On the other hand, in the configuration of Example 2 or Example 3 of the present embodiment, the arrangement of the pressure spring 155 is adopted to offset the increase or decrease in the restoring force F of the pressure spring 155 when the feed roller 101 is displaced from the target position. doing. As a result, the change in the product F·H (moment M) of the restoring force F and the distance H with respect to the displacement of the feeding roller 101 is reduced, so that the variation in the pressing force J of the pressing lever 154 against the arm 102 is suppressed. In other words, even if the rotation angle of the pressure lever 154 slightly fluctuates due to manufacturing tolerances and factors related to the method of controlling the feeding operation, the pressing force K applied to the document by the feeding roller 101 is stabilized to stably feed the sheet. can be realized. In addition, in the present embodiment, the pressure K is automatically adjusted by a mechanical structure. Sheet feeding can be realized.

As shown in FIG. 12(h), in order to further stabilize the pressure K, the product F·H of the restoring force F and the distance H must be maximized within the range in which the feeding roller 101 can move in normal use. It is preferable to have a value (both local maxima and minima). In this embodiment, the range in which the feeding roller 101 can move in normal use is the range in which the height of the upper surface of the document can fluctuate during the feeding operation (that is, from the detection position of the feeding position sensor 191 to range to the lift-up end position).

Further, the change rate of the distance H when the feeding roller 101 is displaced from the target position is set to -2.0 with respect to the change rate of the restoring force F so that the fluctuations of the restoring force F and the distance H are offset in a well-balanced manner. It is preferable that it is in the range of -0.5 or less. The rate of change of the restoring force F and the distance H means the ratio of the variation of the restoring force F and the distance H to the displacement of the feeding roller 101, and the restoring force F and the distance H when the feeding roller 101 is at the target position. refers to the parameter normalized by the value of . In other words, for example, when the feeding roller 101 is displaced from the target position so that the restoring force F increases by 1% (the amount of elongation of the pressure spring 155 increases by 1%), the distance H is 0.5% to 2%. % reduction is acceptable. The rate of change of the restoring force F and the distance H when the feeding roller 101 is displaced from the target position is calculated by, for example, applying the numerical differentiation formula from the values of F and H measured with the amount of displacement being 0 mm and ±1 mm. be able to.

When the pressure spring 155 is arranged below the pressure lever 154 as in the present embodiment, the angle of the line of action G with respect to the horizontal plane perpendicular to the vertical direction is is preferably 30 degrees or less. Such arrangement reduces the area occupied by the pressure spring 155 in the thickness direction of the document, and contributes to miniaturization of the ADF 100 .

(Modification)
In the above embodiment, the compression spring 155, which is a tension coil spring, is used as the elastic member, and the rod-shaped pressure lever 154 extending from the rotating shaft 164 toward the arm 102 is used. These arrangements can be changed as long as . For example, as shown in FIG. 14A, an L-shaped pressing lever 254 having a branched portion for pressing the arm 102 and a portion connected to the pressing spring 155 may be used as the lever member. In this case, the posture of the pressure spring 155 is different from that of the above-described embodiment, and the restoring force F may include an upward component in the vertical direction. Even with such a configuration, if the fixed end 155b of the pressure spring 155 is arranged on the same side as the rotation shaft 164 of the pressure lever 254 with respect to the reference line T0, the feeding roller 101 is moved upward/downward. The distance H respectively decreases/increases when displaced downwards. In other words, a configuration is realized in which the distance H increases or decreases so as to offset the increase or decrease in the restoring force F with respect to the displacement of the feeding roller 101 .

Also, as shown in FIG. 14(b), a compression spring 255 may be used as an elastic member in place of the tension spring. 14(b), the free end 255a of the compression spring 255 presses the pressure lever 154, and the fixed end 255b is supported by the cover body 141. As shown in FIG. At this time, if the fixed end 255b is arranged on the "opposite side" of the rotation shaft 164 with respect to the reference line T0, the distance H decreases/increases when the feeding roller 101 is displaced upward/downward. do. In other words, a configuration is realized in which the distance H increases or decreases so as to offset the increase or decrease in the restoring force F with respect to the displacement of the feeding roller 101 .

An advantage of using a tension spring as the pressure spring 155 is that it is easier to secure a difference between the length during use and the free length than when using a compression spring. In other words, since a spring having a smaller spring constant than a compression spring can be used, it is possible to suppress the fluctuation range of the restoring force with respect to the rotation of the pressure lever 154, thereby stabilizing the pressing force of the feeding roller 101. Cheap.

In addition, a material other than a coil spring (for example, rubber or an air spring) may be used as the elastic member. Further, instead of the structure in which the end of the elastic member is directly connected to the lever member, a structure in which a wire hooked on the lever member is pulled by a torsion coil spring may be used so that the restoring force of the elastic member is applied to the lever member via an intermediate member. You may make it act on.

Further, in addition to the elastic member that produces the pressing force of the feeding roller 101 by the restoring force, a force produced by another configuration may be added to the pressing force of the feeding roller 101 . For example, a weight member may be added so that the weight of the weight is added to the applied pressure. A spring clutch is arranged between the shaft 105 (FIG. 6) of the feeding unit 143 and the arm 102, and as the feeding motor 182 rotates, a constant force is transmitted to the arm 102 via the spring clutch. It may be added to the pressing force of the feed roller 101 .

Further, the arrangement of the pressure lever 154 may be changed, for example, a pressure lever extending in the direction along the sheet feeding direction from a rotation shaft parallel to the axial direction of the feeding roller 101 may be used. The pressing lever 154 and the pressing spring 155 may be moved to the left in FIG. 10 with respect to the feeding roller 101 . Also, two sets of the pressing lever 154 and the pressing spring 155 may be arranged so as to be symmetrical with respect to the axial direction of the feeding roller 101 .

(Other embodiments)
In the above-described embodiment, the case where the present technology is applied to the ADF 100, which is a sheet feeding device for feeding documents in an image reading device, has been described, but it is also applicable to other sheet feeding devices. . For example, the present technology can be applied to sheet feeding devices (20, 21) for feeding sheets P used as recording materials in the image forming unit 301 (FIG. 1).

The present invention supplies a program that implements one or more functions of the above-described embodiments to a system or apparatus via a network or a storage medium, and one or more processors in the computer of the system or apparatus reads and executes the program. It can also be realized by processing to It can also be implemented by a circuit (for example, ASIC) that implements one or more functions.

DESCRIPTION OF SYMBOLS 10... Image forming means (electrophotographic unit)/101... Feeding member (feeding roller)/102... Holding member (arm)/111... Sheet stacking section (document tray)/124, 201... Image reading means (reading unit) )/154, 254 Lever member (pressurizing lever)/155, 255 Elastic member (pressurizing spring)/162 Contact portion (tip of pressurizing lever)/164 Rotating shaft/300 Image formation Device/F: force applied by elastic member to lever member (restoring force of pressure spring)/G: line of action of force/H: distance from rotation axis to line of action of force

Claims (16)

a sheet stacking unit on which sheets are stacked;
Elevating means for lifting and lowering the sheet stacking portion between a stacking position for stacking sheets on the sheet stacking portion and a feeding position above the stacking position for feeding the sheets on the sheet stacking portion. When,
a drive source for driving the lifting means;
a feeding member disposed above the sheet stacking portion for feeding the sheets stacked on the sheet stacking portion;
A holding member for holding the sheet stacking member, wherein the sheet stacking member is held at the sheet stacking unit according to the amount of sheets stacked on the sheet stacking unit. and a second position below the first position where the feeding member contacts the sheet on the sheet stacking section. a holding member for
a lever member that has a contact portion that contacts the holding member and rotates around a rotation shaft;
an elastic member connected to the lever member and biasing the holding member toward the first position via the lever member;
a detection unit that detects a part of the holding member in order to detect the position of the upper surface of the sheets stacked on the sheet stacking unit;
a control unit that controls the drive source based on the detection result of the detection unit;
with
When viewed from the axial direction of the pivot shaft of the lever member, the distance from the pivot shaft to the line of action of the force applied to the lever member by the elastic member when the feeding member is positioned at the first position. but the elastic member is arranged so as to be shorter than the distance from the rotation shaft to the line of action when the feeding member is located at the second position .
A sheet feeding device characterized by: The detection unit is configured to detect that an upper surface of the sheets stacked on the sheet stacking unit is at a height equal to or higher than a detection position,
The control unit is configured to detect that the upper surface of the sheet bundle is at the detection position during execution of a feeding operation in which the sheet bundle made up of a plurality of sheets stacked on the sheet stacking unit is fed one by one by the feeding member. When the detection unit detects that the sheet stack is lower than the detection position, the lifting means raises the sheet stacking unit until the upper surface of the sheet bundle moves to a position above the detection position by a predetermined distance, and the feeding operation is performed. to continue
2. The sheet feeding apparatus according to claim 1, wherein: In the entire range in which the feeding member moves when the upper surface of the sheet stack moves up and down between the detection position and the position above the detection position by the predetermined distance, the lowering of the feeding member is the distance from the pivot axis to the line of action increases;
3. The sheet feeding device according to claim 2, wherein: The detection unit is a photointerrupter that changes detection results in response to the position of the holding member,
The holding member has a flag portion that shields the photointerrupter when the feeding member is positioned at the detection position and does not shield the photointerrupter when the feeding member is lower than the detection position.
4. The sheet feeding device according to claim 2, wherein: When viewed from the axial direction of the rotating shaft of the lever member, the distance from the rotating shaft to the line of action when the feeding member is positioned at the first position is The elastic member is arranged so as to be longer than the distance from the rotation axis to the line of action when positioned at a third position above the first position,
5. The sheet feeding apparatus according to claim 1, wherein: the elastic member is a tension spring having one end attached to the mounting portion of the lever member and the other end fixed;
arranged to contract when the feeding member is lowered from the first position to the second position and to extend when the feeding member is raised from the second position to the first position;
6. The sheet feeding device according to any one of claims 1 to 5, characterized in that: When viewed from the axial direction of the rotation shaft of the lever member, the mounting portion passes through the position of the mounting portion when the feeding member is positioned at the first position, and the mounting portion is moved when the lever member rotates. The other end of the elastic member is positioned on the same side as the rotation shaft with respect to a tangent line that is tangent to the circle to be drawn.
7. The sheet feeding device according to claim 6 , wherein: The angle of the line of action with respect to the horizontal plane is 30 when the other end of the elastic member is positioned below the pivot shaft of the lever member and the feeding member is positioned at the first position. is less than or equal to
7. The sheet feeding device according to claim 6 , wherein: When the feeding member is displaced from the first position, the rate of change of the distance from the rotation shaft to the line of action is - with respect to the rate of change of the force applied by the elastic member to the lever member. a ratio of 2.0 or more -0.5 or less;
The sheet feeding device according to any one of claims 1 to 8 , characterized in that: The product of the magnitude of the force applied by the elastic member to the lever member and the distance from the rotation axis to the line of action has an extreme value inside a range in which the feeding member can move.
The sheet feeding device according to any one of claims 1 to 9 , characterized in that: When viewed from above and below, the lever member extends in a width direction perpendicular to the sheet feeding direction of the feeding member from the abutting portion with respect to the holding member toward the rotation shaft ,
In the sheet feeding direction, a position where the contact portion of the lever member contacts the holding member overlaps with a position of the feeding member in the sheet feeding direction .
The sheet feeding device according to any one of claims 1 to 10 , characterized in that: a conveying roller that conveys the sheet downstream of the feeding member in the sheet feeding direction;
a drive shaft provided on the rotation axis of the transport roller and supplying driving force to the transport roller and the feeding member;
The lever member and the drive shaft are arranged on the same side in the width direction with respect to a feeding unit including the conveying roller, the feeding member, and the holding member.
12. The sheet feeding device according to claim 11, wherein: a frame that supports the sheet stacking portion;
a cover member rotatably supported by the frame and capable of opening and closing a conveying path of the sheet fed by the feeding member;
The lever member and the elastic member are attached to the cover member,
The feeding unit can be attached to and detached from the cover member in a state in which the lever member and the elastic member are attached to the cover member.
13. The sheet feeding device according to claim 12, wherein: The cover member has a cover portion that covers at least part of the lever member and the elastic member,
14. The sheet feeding device according to claim 13, wherein: A sheet feeding device according to any one of claims 1 to 14 ;
image reading means for reading image information from the sheet fed from the sheet feeding device;
An image reading device characterized by: A sheet feeding device according to any one of claims 1 to 14 ;
image forming means for forming an image on a sheet fed from the sheet feeding device;
An image forming apparatus characterized by:

Images